SU‐E‐T‐715: GATE Monte Carlo Simulation of a 6 MV SIEMENS OncorTM Linear Accelerator Photon Beam : Feasibility and Preliminary Dosimetric Study

Purpose : This work is in the context of Monte Carlo simulation in radiotherapy. The objective was to study the modelling of a Siemens OncorTM linear accelerator on the GATE (Geant4 Application for Tomographic Emission) platform. A dosimetric study on water phantom was used to evaluate the reliability and the accuracy of the simulation. Methods: The study had two different objectives: (a) the modelling of the accelerator on the GATE v6.0 platform, and (b) a preliminary dosimetric assessment. Computations were performed in a 70×70×70 cm3 water phantom, with a 100 cm source‐to‐axis distance. The accelerator's components and their geometrical and physical characteristics were defined according to the constructor specifications. The output data were obtained for a dosel (dose scoring voxel, Sarrut & Guigues 2008) of size 2.5×2.5×2.5 mm3 leading to a sensitive volume of 0.015 cm3. A comparative study of the absorbed dose in water calculated by simulation and measured was performed for the following criteria : Photon beam quality TPR (20, 10), i.e the dose ratio at 20 cm and 10 cm in water for a 100 cm source‐detector distance. Depth dose and dose profiles. Output factors for different field sizes. Simulations were performed using a cluster of 26 nodes, 100 CPUs, 194 GB RAM in total. Results: The user interface, based on macros and graphics, facilitates the modelling of different parts of the accelerator. The simulations results obtained with GATE showed a good agreement with actual measurement in water. For example, the photon beam quality obtained by simulation was 0.6725 while the measured one was 0.673. Conclusions: These preliminary results showed good agreement with real measurements. They also are a relevant illustration of the usefulness of GATE v6.0 in the field of radiotherapy. More complex modelling involving the dynamic 160 MLC leaves movements are underway (IMRT).